This disclosure relates generally to internal combustion engines and, more particularly, to ignition devices for internal combustion engines.
Internal combustion engines are well known. Those employing gasoline as fuel typically employ a number of cylinders which compress a gasoline and air mixture such that upon firing of a spark plug associated with each cylinder, the compressed mixture ignites. The expanding combustion gases resulting therefrom move a piston within the cylinder. Upon reaching an end of its travel in one direction within the cylinder, the piston reverses direction to compress another volume of the gasoline and air mixture. The resulting mechanical energy can and has been harnessed for use in myriad applications, foremost among which is the propulsion of vehicles.
Another type of internal combustion engine utilizes the heat generated by highly compressed air to ignite a spray of fuel released into a cylinder during a compression stroke. In such an engine, known as a compression ignition engine, the air is compressed to such a level as to achieve auto-ignition of the fuel upon contact between the air and fuel. The chemical properties of diesel fuel are particularly well suited to such auto-ignition.
The concept of auto-ignition is not limited to diesel engines, however, and has been employed in other types of internal combustion engines as well. For example, it is known to provide a self-igniting reciprocating internal combustion engine wherein fuel is compressed in a main combustion chamber by a reciprocating piston. In order to facilitate starting, each main combustion chamber is associated with a prechamber, particularly useful in starting cold temperature engines. Fuel is injected not only into the main combustion chamber, but the combustion chamber of the prechamber as well, such that upon compression by the piston, a fuel and air mixture is compressed in both chambers. A glow plug or other type of heater is disposed within the prechamber to elevate the temperature therein sufficiently to ignite the compressed mixture. The combustion gases resulting from the ignition are then communicated to the main combustion chamber as well.
Other types of internal combustion engines utilize natural gas as the fuel source. For example, it is also known to provide a compressed natural gas engine wherein a piston reciprocates within a cylinder. A spark plug is positioned within a cylinder head associated with each cylinder and is fired on a timing circuit such that upon the piston reaching the end of its compression stroke, the spark plug is fired to thereby ignite the compressed mixture.
In still further types of internal combustion engines, prechambers are employed in conjunction with natural gas engines. Given the extremely high temperatures required for auto-ignition with natural gas and air mixtures, glow plugs or other heat sources such as those employed in typical diesel engines, are not effective. Rather, a prechamber is associated with each cylinder of the natural gas engine and is provided with a spark plug to initiate combustion within the prechamber which can then be communicated to the main combustion chamber. Such a spark plug-ignited, natural gas engine prechamber is provided in, for example, the 3600 series natural gas engines manufactured by Caterpillar, Inc., the assignee of the present application.
While such engines have proven to be effective, the utilization of spark plugs and fuel enrichment circuits associated with current natural gas engines add cost and complexity to the overall system. In addition, given the usage of spark plugs, the resulting combustion gases include undesirably high levels of pollutants such as nitrous oxide (NOx).
The present disclosure is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
In accordance with one aspect of the disclosure a combustion prechamber assembly is provided which includes a cylinder defining a prechamber, and a piston mounted within the cylinder. The piston is adapted to reciprocate in first and second directions within the cylinder, with movement of the piston in the first direction drawing an air and fuel mixture into the prechamber and movement of the piston in a second direction compressing the air and fuel mixture sufficiently to auto-ignite.
In accordance with another aspect of the disclosure, a method of igniting an engine having a prechamber in fluid communication with a main combustion chamber is provided which includes the steps of drawing a mixture of fuel and air into the prechamber, compressing the mixture of fuel and air sufficiently to cause ignition, and communicating combustion gases resulting from the ignition from the prechamber to the main chamber.
In accordance with another aspect of the disclosure, an engine is provided which includes a main combustion chamber, a prechamber, and a channel. The prechamber is adapted to be in fluid communication with the main combustion chamber and includes a piston adapted to compress a mixture of air and fuel to a point of auto-ignition. The channel connects the prechamber to the main combustion chamber and is adapted to communicate combustion gases from the prechamber to the main combustion chamber.
These and other aspects and features of the disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.